coilset contact problems with a 1940 HRO

[PA0NVD]

I have a 1940 HRO with all the coil sets and started restoring. I replaced all paper caps with orange drops and measures many resistors. Than cleaned all tube sockets and the variable cap. I powered it up at a stabilized 210VDC supply. The receiver worked and the reception was incredible. Low background noise, very sensitive and stable.  All IF transformers were perfectly peaked. and that after 79 years and a VERY abusive trip from Europe to Costa Rica. !!!
But I encountered a problem, many coil sets do not make good contact. I have to move them around to make the receiver work. I tried to adjust the contact springs, but these are quite hard and I am afraid to break them. It improved a little, but the contact problem is still severe. I can push some contact springs slightly down to make the receiver work, so it definitely is an adjustment problem or something similar.
Anyone has encountered this and has a solution?

[WA2SQQ]

If you know for certain that the contacts are making a good mechanical contact, than the contacts themselves may be oxidized. I had a similar problem with a Hammarlund HQ-180's rotary switch. Cleaning didn't help, so i applied a very very small amount of a conductive silver grease to the rotor area. After a few minutes of working the grease in, problem is gone!

[KA0HCP]

http://www.radioblvd.com/National%20HRO.htm

For those not familiar, Henry Rogers, WA7YBS, has an outstanding page on HRO history, restoration and aligning.

[PA0NVD]

Thanks for the link, But I knew that already, indeed an excellent link. Unfortunately they don't address this problem.
It is mechanical, the spring doesn't make mechanical contact. When I press the spring that doesn't make contact slightly down, it works. It looks like the springs have very little movement and are very stiff. The alignment should be really perfect in order to make contact, but the alu cans are not always aligned within a few hundreds of an inch. And it seems that the alignment of the contacts in the coil sets is not that perfect. So with every coil there are other springs that have this problem.

[W3GMS]

I have a 1940 HRO with all the coil sets and started restoring. I replaced all paper caps with orange drops and measures many resistors. Than cleaned all tube sockets and the variable cap. I powered it up at a stabilized 210VDC supply. The receiver worked and the reception was incredible. Low background noise, very sensitive and stable.  All IF transformers were perfectly peaked. and that after 79 years and a VERY abusive trip from Europe to Costa Rica. !!!
But I encountered a problem, many coil sets do not make good contact. I have to move them around to make the receiver work. I tried to adjust the contact springs, but these are quite hard and I am afraid to break them. It improved a little, but the contact problem is still severe. I can push some contact springs slightly down to make the receiver work, so it definitely is an adjustment problem or something similar.
Anyone has encountered this and has a solution?

Nico,

I suggest you contact my good friend Bill-W2DGB. Bill knows the early HRO's in and out.  When he was President of the Antique Wireless Association, he and some of his other colleagues from the AWA visited James Millen.   During that discussion, Mr. Millen donated his personal HRO and his home brew transmitter to the AWA.  Bill then restored James Millen personal HRO and I remember him telling me that he had a finger stock issues with the restoration.  I believe he obtained some material and replaced the faulty contacts.   Bill is not on this site, but I suggest you look up his call on QRZ and send him and email.  I am sure he will respond to you and when I talk with him, I will mention this dialog with you.  

The HRO is a great receiver and I wish you well with it.  

73,
Joe-W3GMS    

[PA0NVD]

Thanks a lot Joe, I will contact him and keep you informed

[Jim, W5JO]

I had a similar problem with my HRO 60 so I found a jeweler who removed the rivets, straightened and retensioned the springs then put them back with rivets he made.  He charged me a very nominal price for the work.

[N3GTE]

I'll mention in passing that there are two different sizes of coil contacts. The very early HROs have small contacts vs the later sets that that are larger. Early would be the first 5 or 6 runs. Something else to have a look at is that there is two plastic glides inside coil box (on the chassis not on the coil set) that support the coils. Could be that they are worn and not holding the coil set up into position. Might try slipping a in washer @ the 4 mounting screws and see if that helps. Have two of the old guys myself a '36 and a '39 seniors. GL  Terry N3GTE

[PA0NVD]

Thanks a lot for the info Terrell, very valuable. I will check tomorrow directly the size of the contacts, that may be the case because I bought several coil sets separately. The sliders are ok, perhaps I can raise them a little like you suggested.

[N3GTE]

Would check the two end cans on the coil packs for physical damage. Could be pushed in a bit lowering the amount of lift from the glide. If you need to remove any of the coils from the pack you just want to loosen the four screws (two on the top and two on the bottom of each coil). You don't need to remove them as they act as a clamp.

Some other coil notes. It seem that the later coils from the HRO -7 and newer don't seem to have reverse compatible w/ the sets w/the older standard base tubes (6 pin jobs) and the octal tubes. Well at least the oscillator coil. I was searching a D coil pack and the only thing I could find and for a '7. Thought that would be ok but after remounting them into a suitable panel I could get the osc section work across the entire band. I replaced the osc coil w/ an older one and got evening working fine. Methinks the feedback level is lower on the new coils.

Gotta love those bandspread coil set. Something like 9 linear feet coverage for the ham bands.

GL
Terry

[PA0NVD]

You found it Terry. The customs in Puerto Limon did open my container with stuff, robbed a whole lot and did throw everything around, including the box with coil packs. Several coils had physical damage and dents wich I repaired. Your suggestion to check the two end cans was right on. I did put a ruler over the contacts and sure enough there was too much difference in height between the center cans and the end cans. I did rectify a few coil packs and they are working ok now. Thanks a lot.
During alignment the digital readout I made really did help me a lot. I am really impressed by the reception, VERY nice receiver.

[N3GTE]

Glad you got it sorted!
If you have an interest I have collected many HRO articles from many magazines from the 30's thru 2013 or so. Would be happy to pass them along if could send me your email address to:tbs50a@aol.com

Terry